1. Field
Exemplary embodiments of the present invention relate to a semiconductor device fabricating technology, and more particularly, to a semiconductor device with buried bit lines and a method for fabricating the same.
2. Description of the Related Art
As the degree of integration of a semiconductor memory device has increased, in order to reduce a plane area occupied by a unit cell, a cell structure has been changed from 8F2 and 6F2 to 4F2 (F2: cell size factor). Various methods for forming other component elements such as transistors/bit lines, word lines, capacitors, etc, in step with such reduction in the area of the unit cell have been suggested. In particular, in order to realize a 4F4 cell structure, a vertical channel semiconductor device has been proposed, in which a source and a drain are disposed up and down to induce a vertical channel.
In the vertical channel semiconductor device, a gate electrode is formed around an active pillar which vertically extends from the main surface of a substrate and a source and a drain are formed in the upper and lower parts of the active pillar with the gate electrode disposed therebetween, by which a channel is vertically formed from the main surface of the substrate. Accordingly, even when the area of the semiconductor device is reduced, a channel length may not be adversely influenced.
In realizing the vertical channel semiconductor device in this way, a buried bit line structure has been disclosed, in which a bit line is buried under an active pillar.
In the conventional art, a buried bit line is formed in such a way that impurity ions are implanted into a substrate between active pillars to form an impurity region and the substrate is etched between the active pillars to separate the impurity region. However, the resistance of the buried bit line may increase due to limitations in the doping concentration of the impurity.
Although the resistance of the buried bit line may be reduced by forming the buried bit line using a metallic layer with low resistance, it may be difficult to apply such a method in terms of a structural aspect. For instance, in order to use a metal as a buried bit line, a method has been suggested, in which a buried bit line is formed by forming a contact (so called a one side contact: OSC) in such a way as to expose one sidewall of an active pillar. Nevertheless, the buried bit line with the OSC structure may have a complicated fabrication procedure, and require high difficulty fabricating technologies, and thus, it may be not easy to adapt the method for mass production.